Behaviour of the energy dissipation coefficient in a rough wall turbulent boundary layer

Abstract

Hot-wire anemometry measurements are made in a rough wall turbulent boundary layer to assess the dependence of the mean turbulent kinetic energy dissipation coefficient, Cε, on the distance from the wall and the Taylor microscale Reynolds number, Reλ. The locally isotropic expression ⟨ εiso⟩ is used as a surrogate for the mean turbulent kinetic energy dissipation rate, ⟨ ε⟩ , for calculating Cε= ⟨ ε⟩ L/ u′ 3; L and u′ are the integral length scale and the rms of the longitudinal velocity fluctuation, respectively. The measurements show that Cε varies significantly near the wall, but becomes almost constant in the region 0.2 ≤ y/ δ≤ 0.6 of the boundary layer, a region where Reλ is also practically constant.